1. Field of the Invention
The present invention relates to a method for forming contacts in a semiconductor device.
2. Description of the Prior Art
For obtaining a higher integration degree in a semiconductor device, contact holes formed to be in contact with a semiconductor substrate or a conduction layer have a reduced dimension. The increase in integration degree results in a great increase in topology.
Referring to FIGS. 1A to 1C, a conventional method for forming contacts is illustrated.
In accordance with this method, conduction layers 2, 3 and 4 are sequentially formed, in this order, on a silicon substrate 1, as shown in FIG. 1A. The conduction layers 2, 3 and 4 are insulated from one another by an insulating film 5. Thereafter, the insulating film 5 is then etched using a mask pattern formed on the insulating film 5 such that the silicon substrate 1 is partially exposed, thereby forming contact holes. Subsequently, a deposition material is deposited in the contact holes, thereby forming contacts.
Various methods may be used for formation of contact holes achieved by etching the insulating film 5.
For example, a method may be used which involves two etching steps one being a wet etching and the other being a dry etching. By the combination of the wet etching and the dry etching used in formation of contact holes as shown in FIG. 1B, the upper portion of each contact hole is etched to have a wine glass shape and, thus, an increased width. Thereafter, a treatment for providing a good step coverage of the conduction material is carried out. As the treatment for providing the good step coverage, a dry etching process may be used upon etching the insulating film 5 to form contact holes as shown in FIG. 1C. By this dry etching process, the upper portion of each contact hole has an increased width. In FIGS. 1B and 1C, the reference numeral 6 denotes contact hole portions subjected to the wet etching whereas the reference numeral 7 denotes contact hole portions subjected to the slant dry etching.
However, such conventional methods for forming contact holes by using the combination of a wet etching and a dry etching and by using a dry etching have a problem of a poor step coverage caused by a high topology between the upper and lower portions of each contact hole formed. Due to such a poor step coverage, the resistance of the contact material may be adversely increased. In a severe case, a short circuit may occur.